Formaldehyde and succinaldehyde gelatin hardening composition and method of hardening therewith



United States Patent 3,226,849 FORMALDEHYDE AND SUCCINALDEHYDE GEL- ATIN HARDENING COMPOSITION AND METH- 0]) OF HARDENING THEREWKTH Harry C. Baden and Charleton Cordery Bard, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Oct. 10, 1963, Ser. No. 315,336 7 (Ilaims. (Cl. 96-111) This application is a continuation-in-part of our application Serial No. 173,820, filed February 16, 1962, and now abandoned.

This invention relates to the use of a mixture of formaldehyde and succinaldehyde for hardening gelatin.

Various materials have been suggested for hardening gelatin. As a rule the effect a mixture of those hardeners exhibit is no more than the sum of their individual effects. Formaldehyde alone as a prehardener in the processing of color emulsions containing couplers has generally been undesirable because formaldehyde is prone to react with the incorporated coupler. These emulsions are of the coupler-containing gelatin-silver halide photographic emulsion type. Recent discoveries however have made possible the use of formaldehyde as a prehardener for the incorporated coupler emulsions resulting in satisfactory sensitometric properties. A procedure of this type permitting the use of formaldehyde hardener has been described in U.S. application Serial No. 111,489 of Blackmer and Vogt, filed May 22, 1961, and now U.S. Patent 3,168, 400.

Formaldehyde has been considered useful in prehardening the gelatin of black and White gelatin-silver halide photographic emulsions but high concentrations of formaldehyde such as on the order of 55 grams per liter have ordinarily been necessary to adequately harden the gelatin at a relatively low pH such as 4-6 as is used in some photographic processing operations. The use of formaldehyde and other aldehyde hardeners in high concentrations has offered various disadvantages the least of which has been irritation of the eyes and respiratory passages of the operators of the process.

Aliphatic dialdehydes have been known to harden gelatin at a low pH but only succinaldehyde of these aldehydes has been considered suitable for use in silver halide color photography using incorporated couplers because of the adverse sensitometric effects from some of the other dialdehydes in this type of color photography. However substantial concentrations of succinaldehyde is often required for hardening gelatin in certain operations thus making its use in those situations economically and physiologically disadvantageous. The high concentration of succinaldehyde which has been considered necessary in certain prehardening baths has necessitated the use of considerable concentrations of scavenger (for instance, hydroxylamine sulfate) in the neutralizing bath, the use of which is described in the Blackmer and Vogt application supra.

An object of our invention is to provide a procedure for hardening gelatin. Another object of our invention is to provide a procedure for prehardening gelatin-silver halide photographic emulsions prior to their development using diminished quantities of aldehyde hardener. A further object of our invention is to provide a procedure for hardening gelatin particularly in the form of gelatinsilver halide photographic emulsions using a mixture of certain aldehydes which have been found to exhibit a synergistic effect in the hardening of gelatin. A still further object of our invention is to provide a method hardening photographic emulsion layers prior to their processing which results in a material decrease in the amount of scavenger or neutralizer necessary in the succeeding bath to neutralize the effect of the retained hardencrl Other objects of our invention will appear herein.

We have found that formaldehyde and succinaldehyde used in combination in the hardening of gelatin exhibit unusual and unique properties making that combination particularly effective in that capacity. We have found that a mixture of formaldehyde and succinaldehyde when used for prehardening gelatin-silver halide emulsions prior to processing exhibits a synergistic effect upon the gelatin which makes possible the use of relatively low concentrations of hardener especially at a pH within the range of 4-6. 1

In its broadest aspects our invention involves the treat ment of a gelatin composition with succinaldehyde'and formaldehyde to obtain a pronounced hardening effect with the quantities of aldehyde used.- Our invention in-- volves particularly the prehardening of gelatin-silver halide emulsions with a bath having a diminished concentration of both formaldehyde and succinaldehyde' whereb y, the

swelling of the photographic layers of the photographic film treated therewith is considerably decreased in processing compared with the sum of the separate effects of these aldehydes used in the corresponding concentrations.

As a useful modification of our invention the gelatin may be treated with succinaldehyde such as by incorporating succinaldehyde into the gelatin composition and then treating it subsequently with formaldehyde.

The hardener in accordance with our invention is particularly effective at the low pH which is desirable in those processing operations which are carried out at an acid pH. However, the invention is not limited to operating at an acid pH as hardening effects on gelatin with this combination can be obtained within a pH range of 2-12. When the hardener in accordance with our invention is used as a prehardener for the gelatin layers of a photographic product the succinaldehyde-formaldehyde mixture is incorporated in a prehardening formula such as in conjunction with sodium sulfate or the like which prehardener is employed in treating the gelatin layers. In the case of an aqueous solution of gelatin the hardener may be incorporated in the gelatin composition or the aqeuous gelatin may be treated first with succinaldehyde and followed by treatment with formaldehyde such as after the succinaldehyde modified gelatin has been coated out in the form of a layer upon a support. With the use of an aqueous solution of a mixture of formaldehyde and suc cinaldehyde an excellent hardening effect on gelatin is obtained with compositions in which the formaldehyde has a concentration of 515 grams per liter and the succinaldehyde of 05-10 grams per liter. After the photographic layer has been hardened the product containing such layer, for instance a photographic film containing same, is desirably treated with a neutralizer such as hydroxyl amine sulfate as described in Blackmer and Vogt application Serial No. 111,489. The photographic material is then ready for processing and the gelatin-silver halide photographic emulsion which had been so treated shows only a relatively small amount of swelling.

This method of hardening gelatin is particularly advantageous in processing film in a rapid processing operation wherein the prehardening should be no more than a matter of minutes. Due to the synergistic effect exhibited by the mixture of formaldehyde and succinaldehyde a quick hardening of the gelatin layers is obtained. If the gelatin is treated before forming a layer therefrom the aqueous solution of gelatin may be conveniently mixed with succinaldehyde-formaldehyde or it may be mixed with succinaldehyde and the layer resulting from coating out the gelatin composition onto a surface may be hardened by treating with aqueous formaldehyde or gaseous formaldehyde either before or after the gelatin layer has 3 been dried. The following examples illustrate our invention:

Example 1 Photographic films containing a layer of gelatin-silver halide photographic emulsion with incorporated coupler characteristic of emulsions used in color photography were after exposure put through several processing operations respectively wherein the films were subjected to a prehardener corposition for 125 seconds at 125 F. and then to neturalizer (hydroxylamine sulfate) for 25 seconds. The films were then subjected to rapid development for 100 seconds, stop bath for 25 seconds and washing for 25 seconds all at 100 F. The maximum vertical swell at the end of the final wash was used as the measure of the degree of hardening. The prehardener compositions used and the degree of swell of each of the films were as follows:

1 As required.

Result No. 3 shows that the combination of 1 gram per liter of succinaldehyde and 9.2 grams of formaldehyde per liter increased the degree of hardening (reduction of swell) more than twice that obtained by the formaldehyde in the absence of the succinaldehyde.

After the films had been subjected to prehardening and neutralizing, they were each processed in conventional manner such as by the developing process described in Blackmer and Vogt application Serial No. 111,489.

Prehardening of gelatin-silver halide photographic emulsions used in black and white photography with succinaldehyde-formaldehyde containing prehardener compositions exhibits results superior to those obtained using either aldehyde separately in the prehardening bath preliminary to the developing operation.

Example 2 10 grams, dry weight, of deionized gelatin were dispersed 85 grams of water at 40 C. and the pH was adjusted to 65. 5 ml. of a 0.1 M succinaldehyde solution were stirred into the gelatin solution thus giving a solution containing 0.05 mole of succinaldehyde per gram of gelatin. A similar preparation was carried out using gelatin with its natural salt content and succinaldehyde concentrations of 0.05 and 0.025 mole per gram of gelatin. The above were alkali processed gelatins having a viscosity at 6 /s% concentration of 7.6 and 7.3 cps. re

spectively. These gelatins when treated with formaldehyde showed greately increased hardening and were quickly and effectively hardened, in contrast to gelatins which had been treated with formaldehyde only. The formaldehyde was effective in proportions as little as 0.005 M and was particularly effective when used upon a gelatin layer or layers where the gelatin was first modified with succinaldehyde such as after a minute treatment and then treated with formaldehyde. The invention is especially useful for increasing the physical properties of gelatins when lowered viscosity products are used. By our invention the properties of the gelatin particularly of a low grade type are appreciably improved.

We claim:

1. A prehardening composition for photographic products comprising an aqueous solution of a mixture of formaldehyde and succinaldehyde, the former in 0.5- 1.5% concentration and the latter in 0.051.0% concentration therein.

2..A prehardening composition containing per liter of aqueous solution 9.2 grams of formaldehyde and 1 gram of succinaldehyde.

3. A method of processing exposed photographic film which comprises prehardening the film with a mixture in aqueous solution of 5-15 parts of formaldehyde and 0.5 10 parts of succinaldehyde, and then treating with a neutralizing bath followed by subjecting the film to development in a bath adapted thereto.

4. A method of improving the properties of gelatin which comprises treating said gelatin in aqueous form with a combination of 05-10 parts succinaldehyde and 5-15 parts of formaldehyde.

5. A composition for use in treating photographic gelatin layers composed of an aqueous solution of sodiurn sulfate, 5-15 parts of formaldehyde and 05-10 parts of succinaldehyde.

6. The method which comprises treating a gelatin layer with a combination of 0.51() parts of succinaldehyde and 5-15 parts of formaldehyde under aqueous conditions.

7. The hardening of a gelatin-silver halide emulsion layer which comprises treating the emulsion with both 0.5-10 parts of succinaldehyde and 5-15 parts of formaldehyde in aqueous solution whereby a synergistic hardening effect is obtained.

References Cited by the Examiner UNITED STATES PATENTS 2,414,858 1/1947 Davidson 96l 11 2,868,773 1/1959 Kress 2601 17 3,012,886 12/1961 Lerner 260-117 FOREIGN PATENTS 588,451 12 /1959 Canada.

NORMAN TQRCHIN, Primary Ex mliller. 

1. A PREHARDENING COMPOSITION FOR PHOTOGRAPHIC PRODUCTS COMPRISING AN AQUEOUS SOLUTION OF A MIXTURE OF FORMALDEHYDE AND SUCCINALDEHYDE, THE FORMER IN 0.51.5% CONCENTRATION AND THE LATTER IN 0.05-1.0% CONCENTRATION THEREIN. 